Expression of the Plastid ndhF Gene Product in Photosynthetic and Non-Photosynthetic Tissues of Developing Barley Seedlings

A fragment of the NDH-F subunit of the plastid NAD(P)H dehydrogenase complex (NAD(P)H-plastoquinone-oxidoreductase) from barley was expressed as a fusion protein in Escherichia coli and an antibody to the fusion protein was prepared. Western blot analysis using the anti-NDH-F antibody showed specificity towards a plastid polypeptide of approximately 70 kDa present in both photosynthetic and non-photosynthetic barley tissue. The polypeptide was found in thylakoid membranes of green leaves whereas in etiolated leaves it was shown to be associated with the membrane fraction of etioplasts. NDH-F levels were higher in roots and etiolated tissue than in greening or young leaves. During leaf ontogeny, NDH-F levels decreased from young to mature tissue but increased during senescence. The accumulation of NDH-F in thylakoids of young leaves was stimulated by photooxidative treatment. The results indicate a high degree of expression of plastid ndh genes (which encode NAD(P)H dehydrogenase subunits) in non-photosynthetic plastids and under conditions which impair the photosynthetic activity of chloroplasts. In addition to its putative implication in photosynthetic electron transport, a non-photosynthetic role, such as chlororespiration, is proposed for the plastid NAD(P)H dehydrogenase complex.